Photographic film unit

ABSTRACT

A self-developing film unit including a photosensitive sheet, a transparent second sheet, binding means for securing the sheets in face-to-face relation at the margins thereof with the trailing end section of the second sheet extending beyond the trailing edge of the photosensitive sheet, a container of processing liquid coupled with the sheets at one end of the film unit in position to release its contents for spreading between the sheets, and trapping means at the opposite end of the film unit for collecting and retaining excess processing liquid. The film unit is adapted to be retained intact following spreading of the processing liquid and the trapping means include narrow portions of the trailing end section embossed toward the photosensitive sheet to form longitudinal ribs providing liquid trapping spaces located between the trailing end section of the second sheet and the binding means.

United States Patent [72] inventor Frank W. Knight Salem, NH. [21] Appi. No. 787,749 [22] Filed Dec. 30, i968 [45] Patented Nov. 9, 1971 [73] Assignee Polaroid Corporation Camblidge, Mass.

54 PHOTOGRAPHIC FILM UNIT 13 Claims, 5 Drawing Figs.

[52] U.S. Cl 96/76 R 6019c 1/48 [50] Field of Search 96/76, 77

[56] References Cited UNITED STATES PATENTS 2,627,460 2/l953 Land 96/76 X 2,659,825 ll/l953 Land 96/76 X 2,689,716 8/l954 Land 96/29 2,686,717 8/1954 Land 96/76 X 2,698,243 12/1954 Bachelderetal. 3,320,065 5/1967 Campbell .i

ABSTRACT: A self-developing film unit including a photosensitive sheet, a transparent second sheet, binding means for securing the sheets in face-to-face relation at the margins thereof with the trailing end section of the second sheet extending beyond the trailing edge of the photosensitive sheet, a container of processing liquid coupled with the sheets atlone end of the film unit in position to release its contents for spreading between the sheets, and trapping means at the opposite end of the film unit for collecting and retaining excess processing liquid. The film unit is adapted to be retained intact following spreading of the processing liquid and the trapping means include narrow portions of the trailing end section embossed toward the photosensitive sheet to form longitudinal ribs providing liquid trapping spaces located between the trailing end section of the second sheet and the binding means.

PATENIEnunv 9 mm sum 1 6r 2 INVENTOR. FRANK W. KNIGHT llwum a/rwl W anwl ATTORNEYS FIG.3

INVENTOR. FRANK w. KNIGHT 6W MW W S. M

ATTORNEYS PIIOTOGRAPIIIC FILM UNIT The present invention is illustrated as incorporated in a film unit of the type shown and described in the copending U.S. Pat. application of Edwin H. Land et al., Ser. No. 622,286, filed March 10, I967, abandoned and replaced by application Ser. No. 5,799, filed Jan. 26, I970, adapted to be processed to produce a photographic print, preferably in full color, by a diffusion transfer process. As previously noted, film units of this type generally include a photosensitive sheet, a transparent second or image-receiving sheet through which the photosensitive sheet is exposed and an image formed between the sheets is viewed, binding means secured around the margins of the sheets to retain them in face-to-face relation during exposure and subsequent processing and viewing, and a rupturable container of a viscous processing liquid attached to the sheets, the liquid adapted, when distributed between the sheets in contact with the exposed photosensitive material, to produce 7 a diffusion transfer image, preferably in full color, visible through the transparent second sheet. Processing of the film unit is accomplished by passing it between a pair of juxtaposed pressure-applying members, beginning with the container, to rupture the container and spread its liquid contents in a layer within the film unit toward the opposite end thereof (termed the trailing end) to efiectuate positive image formation by a diffusion transfer process. The processing liquid adheres together the layers of the film unit between which it is spread to form a laminate and contains an opacifying agent providing a background for the transfer image formed between the layer of processing liquid and the transparent second sheet. The laminate thus formed contains a protectively enclosed image and is retained intact thereafter as a photographic print.

The processing liquid distributed in a layer within the film unit includes a viscous aqueous alkaline solution adapted to initiate a diffusion transfer process involving the formation of an imagewise distribution of image-providing substances in an exposed photosensitive layer and transfer of the image-providing substances by diffusion to a juxtaposed, image-receiving layer where they form a visible image. In order to insure that a predetermined exposed area to be processed is completely covered by a layer of predetermined uniform thickness of the aqueous alkaline processing composition, it is the usual practice to supply, in the container, a quantity of liquid in excess of the minimum amount required. For this reason, and because of the highly viscous and caustic nature of the liquid processing composition which presents a danger to both the user of the film unit and the apparatus in which it is employed, it is important that means be provided for collecting and retaining excess processing liquid within the film unit so as to prevent escape of the liquid from the film unit during and subsequent to spreading therewithin. I-leretofore, it has been the practice to prevent overrun and escape of the. processing liquid beyond the trailing ends of the sheets (as well as at their lateral margins) by extending the trailing end portions of the sheets and providing spacing elements between the extended end portions of the sheets adapted to space apart the pressureapplying members employed to spread the processing liquid during movement of the extended trailing end portions of the sheets between the pressure-applying members and thereby provide a liquid reservoir between the extended trailing end portions in which excess liquid is collected and retained. The extent that the trailing end portions are extended is dependent upon both the amount and distribution of the excess liquid and must be of sufiicient length to retain all excess liquid spread beyond the distal edges of the areas of these sheets to be processed.

The film unit of the invention differs from the usual prior art film unit in two important respects which materially alter and increase the seriousness of the problems of collecting and retaining excess processing liquid. In the present film unit, the

layer containing the diffusion transfer image is not separated from the processed photosensitive layer and/or the layer of processing liquid, but the film unit is maintained intact as a laminate following processing with the image-containing layer sandwiched between two outer support layers or sheets; and

the sheets of the film unit are bound to one another at their margins by a sheet material which forms the margins of the finished photographic print and, accordingly, is relatively narrow as compared to the size of the image area. This latter structural feature requires that provision must' be made for releasing air at the trailing end of the film unit so that it does not become trapped and interfere with liquid distribution; and means that the space within the film unit at the trailing end thereof available for collecting and retaining excess processing liquid not only is extremely limited but is very close to, if not in direct communication with, the region of the laminate between the outer support sheets containing the visible positive image. Thus, the problem of providing sufficient space or volume within the film unit in which to collect and retain the excess processing liquid is increased, while there are created the additional problem of preventing fiowback of the excess processing liquid into the image area and the problem presented by a reservoir of excess processing liquid located immediately adjacent the image area where it is available to migrate back into the image area to discolor or otherwise impair the visible image.

An object of the invention is to provide in a film unit of the type described, novel and improved means for collecting and retaining excess processing liquid in a relatively small space while releasing air from the film unit, assuring that the liquid is preventedfrom escaping from the film unit and that excess liquid does not flow back or migrate back into the image area of the film unit. Another object of the invention is to provide means for collecting and retaining excess processing liquid comprising integral portions of one of the photosensitive and second sheets and the binding sheet securing said sheets in face-to-face relation with said trailing end section of one of said sheets extending beyond the trailing edge of the other of said sheets resulting in a substantial cost reduction due to a saving in sheet material and reduction in the number of components. 7

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the product possessing the features, properties and the relation of components which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

' FIG. 1 is a perspective view, partially in section, showing a film unit embodying the invention;

FIG. 2 is an exploded, perspective view of the components of the film unit of FIG. 1;

FIG. 3 is an enlarged longitudinal, sectional view of the trailing end portion of the film unit, the section being taken through a longitudinal rib; and v FIGS. 4 and 5 are enlarged, sectional views taken between longitudinal ribs, showing the trailing end portion of the film unit in which excess processing liquid is collected and retained and illustrating the way in which the film unit performs this function.

The film unit of the invention adapted to the performance of a number of different image-forming processes and particularly to the production of a positive photographic print preferably in full color produced by a diffusion transfer process in which a photographic image-recording medium including a photosensitive material such as silver halide is exposed to form an image (latent) therein and is treated by wetting with a liquid processing agent to develop the image in the image-recording medium, form an imagewise distribution of transferable image-providing substances and transfer the image-providing substances by diffusion to an image-receptive stratum in which they are immobilized to form a visible positive image. The film unit may comprise materials for produc ing a black-and-white print according to a process such as dis closed in the U.S. Pats. of Edwin H. Land, No. 2,543,181, granted Feb. 27, 1951, and No. 2,662,822, granted Dec. 15, 1953. In this embodiment, the film unit may comprise an image-recording medium including, as the photosensitive material, a silver halide emulsion; a liquid processing agent including a silver halide developer and a silver complexing agent; and the material required to provide a silver precipitating environment in an image-receptive stratum of the film unit during processing. The processing liquid is distributed in contact with the layer containing the exposed image-recording medium for permeation therein to develop the latent image and form a soluble silver complex from unexposed silver halide which is transferred by diffusion to an image-receiving stratum where it is reduced to silver in the presence of a silver precipitant to form a visible positive image. The silver precipitating environment may be provided initially as a layer or stratum on one of a pair of superposed elements comprising the film unit, preferably an element different from the one including the image-recording medium, and/or in the liquid composition distributed in a layer between the elements.

A preferred embodiment of the film unit of the invention includes all of the materials and reagents required to produce a full color photographic print by a process such as disclosed in U.S. Pat. No. 2,983,606, issued May 9, 1961, in the name of Howard G. Rogers. This patent discloses a photosensitive element including a silver halide emulsion and a dye developer, that is, a dye which is a silver halide developing agent; a second or image-receiving element including an image-receiving layer of a dyeable material; and a processing liquid in which the dye developer is soluble. The photosensitive and image-receiving elements are superposed with the emulsion and image-receiving layers in face-to-face relation and the processing liquid is distributed in a uniform layer between and in contact therewith for permeation into the photosensitive layer where it initiates development of exposed silver halide. The dye developer is immobilized or precipitated in exposed areas as a consequence of development while in unexposed areas and partially exposed areas of the emulsion, the dye developer remains unreacted and diffusible thereby providing an imagewise distribution of unoxidized dye developer which is transferred, at least in part, by diffusion to the image-receiving layer without altering the imagewise distribution of the dye developer, to form a reversed or positive color image of the developed latent image in the emulsion. Multicolor transfer images are obtained utilizing dye developers, for example, by employing an integral multilayer photosensitive element such as illustrated in FIG. 9 of U.S. Pat. No. 2,983,606 including at least two selectively sensitized overlying photosensitive strata on a single support. A typical photosensitive element of this type comprisesa support carrying a red sensitive silver halide emulsion stratum, a green sensitive silver halide emulsion stratum, and a blue sensitive silver halide emulsion stratum, the emulsions having associated therewith, respectively, for example, a cyan dye developer, a magenta dye developer, and a yellow dye developer. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlayers formed, for example, of gelatin or polyvinyl alcohol. In the example given, the dye developers are preferably selected for their ability to provide colors useful in producing a full color image by a subtractive process and may be incorporated in the respective silver halide emulsion with which they are associated or in a separate layer behind their respective silver halide emulsion. In certain instances, a yellow filter is incorporated, located in front of the green sensitive emulsion and comprising a yellow dye developer or a separate layer ofa yellow filter material.

Reference is now made to FIGS. 1, 2, and 3 of the drawings, wherein there is illustrated a photographic film unit 10 embodying the invention, the thickness of the materials being exaggerated for purposes of clarity of illustration. Film unit 10 comprises a photosensitive or image-recording sheet 12, a second or image-receiving sheet 14, and a rupturable container 16 holding a quantity of processing liquid 18. Sheets 12 and 14 are preferably, although not necessarily, rectangular and substantially the same width and are arranged in superposed face-to-face contact with at least the lateral edges of each sheet aligned with the lateral edges of the other. The two sheets are retained in superposed relation by a binding element 20 in the form of a rectangular sheet larger than either of the photosensitive or image-receiving sheets and secured to the two sheets at the margins thereof. Binding element 20 is in the general form of a frame having a large rectangular opening 22 defining the extent of the image produced in the film unit, surrounded by lateral edge portions 24 and leading and trailing end portions 26 and 28 respectively. Sheet 12 includes lateral marginal portions 30 and a trailing end section 34, and sheet 14 includes lateral marginal portions 32 and a trailing end section 36. Sheet 14 is longer than sheet 12 so that the trailing end section of sheet 14 extends beyond the trailing edge of sheet 12. The lateral edge portions 24 of binding element 20 are secured around and to, respectively, the outer surfaces of lateral marginal portions 30 and 32 of sheets 12 and 14, and trailing end portion 28 of element 20 is secured to trailing end section 36 of sheet 14, folded around the trailing edge of sheet 14 and secured to the outer surface of trailing end section 34 of sheet 12, the sheets effectively binding the two sheets to one another along three sides thereof. In a preferred form of film unit adapted to produce a reflection print surrounded by a white border and viewed against a white background, at least binding element 20 is formed of an opaque, white material and container 16 may also include a white outer coating to provide a more aesthetically pleasing product.

Container 16 is of the type shown in U.S. Pat. No. 2,543,181, formed by folding a rectangular blank of a fluidimpervious sheet material medially andsealing and sealing marginal sections of the blank to one another to form a cavity for containing processing liquid 18. The seal between longitudinal marginal sections 38 of the container is weaker than the end seals so that upon the application of a predetermined compressive force to the walls of the container in the region of the liquid-filled cavity, there will be generated within the liquid hydraulic pressure sufficient to separate longitudinal marginal sections 38 throughout the major portion of their length to form a discharge mouth at least equal in length to the length of the cavity and the width of opening 22 through which processing liquid 18 is discharged. Container 16 is attached to the sheets at the edges (leading) thereof opposite trailing end portions 34 and 36, preferably with the longitudinal edge of the container located at least closely adjacent the leading edges of the sheets and with the discharge passage of the container aligned with the facing or inner surfaces of the sheets. Sheets 12 and 14 include, respectively, leading end marginal portions 40 and 42 and the means for coupling the container to the sheets include end portion 26 of binding element 20 secured to leading end marginal portion 42 of sheet 14 and longitudinal marginal sections 38 of the container so as to bridge the container and sheet 14; and a strip 44 secured to leading end marginal portion 40 of sheet-12 and the other longitudinal marginal section 38 of the container to bridge the gap between the container and sheet 12. The binding element and strip 44 cooperate to provide a the scope seal between the marginal sections of the container defining the discharge mouth thereof and sheets 12 and 14; and form a conduit for conducting the liquid from the container between the sheets at leading end marginal portions 40 and 42 thereof.

The most useful and advantageous film unit insofar as packaging, storing, handling, exposure and processing are concerned, is one characterized by an integral, unitary, laminate form of structure designed so that its integrity may be maintained during and after exposure and processing; and a structure that is sturdy, has some flexibility, and can be handled and manipulated by mechanical means without damage to produce a useful and attractive photographic print.- A useful and attractive photographic print can be described as being substantially flat or planar and without a tendency to curl as the result of temperature and humidity changes; as being relatively rigid and inflexible as opposed to being limp or easily bent; as having a uniform white border surrounding a welldefined rectangular image that extends to the border; and a protective coating or covering for the image permitting the print to be handled and stored without the necessity for taking special precautions to avoid damage and deterioration. The structure and composition of components of the film unit of the invention combine to provide a film unit meeting these criteria and specially adapted, when processed, to provide a useful and attractive photographic print, preferably in full color, having the foregoing characteristics.

In order to provide a rigid durable structure having an integrity which is maintained from the time of assembly (during manufacture) to the finished print and providing a protective environment for the photosensitive medium as well as the final image, while permitting exposure of the photosensitive medium and viewing of the final image, at least one of the sheets of the film unit is formed of a transparent material. In the embodiment shown the second or image-receiving sheet is transparent and the photosensitive medium is exposed and the final image is viewed through the image-receiving sheet which functions to protect both the image-recording medium and the final image. ln other embodiments of the film unit, the photosensitive sheet may be transparent depending upon the manner in which the image-recording medium is exposed and the final image is formed and viewed. The transparent imagereceiving sheet may be formed of a conventional film base material such as cellulose triacetate coated on its inner surface with one or more layers providing an appropriate environment for the formation of a diffusion transfer image. In a film unit designed to produce a color image in terms of a dye developer, the image-receiving sheet may be prepared as disclosed in the following example, by coating a transparent cellulose triacetate film base in succession with the following layers:

l. the partial butyl ester of polyethylene/maleic anhydride copolymer prepared by refluxing, for 14 hours, 300 grams of high viscosity poly-(ethylene/maleic anhydride), 140 grams of n-butyl alcohol and 1 cc. of 85 percent phosphoric acid to provide a polymeric acid layer approximately 0.75 mils thick;

2. a solution of hydroxypropyl cellulose in water to provide a polymeric spacer layer approximately 0.075 mils. thick; and

. a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4- vinylpyridine, at a coverage of approximately 600 mgs./ft., to provide a polymeric imagereceiving layer approximately 0.40 mils. thick.

In a preferred embodiment of the film unit, useful in color i photography and incorporating an image-receiving sheet prepared as described above, the image-receiving sheet prepared as described above, the image-recording sheet is preferably opaque to actinic light and is prepared, for example, by coating in succession on a gelatin subbed opaque cellulose triacetate film base, the following layers:

l. a layer of cyan dye developer l,4-bis-(B-[hydroquinonyla-methyl]-ethylmino)-5,8-dihydroxy-anthraquinone dispersed in gelatin and coated at a coverage of about 150 mgs./ft. ofdye and about 200 mgs./ft. of gelatin; and

2. a red-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 200 mgs./ft. of silver and about 100 mgs./ft. ofgelatine;

a layer of gelatin coated at a coverage of about 200 mgs./ft.

4. a layer of the magenta dye developer Z-(p-[B-hydroquinonylethyl]-phenylazo)-4-isopropoxy-1-napthol dispersed in gelatin and coated at a coverage of 70 mgs./ft. of dye and about 100 mgs./ft. ofgelatin;

5. a green-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 100 mgs./ft. of silver and 60 mgs./ft. of gelatin;

a layer of gelatin coated at a coverage of about 150 mgs./ft.

7. a layer of the yellow dye developer 4-(p-[B-hydroquinonylethylJ-phenylazo)-3-(N-n hexylcarboxamido)-lphenyl-S-pyrazolone dispersed in gelatin and coated at a coverage of about 40 mgs./ft. of dye and 50 mgs./ft. of gelatin; 1

8. a blue-sensitive gelatino-silver iodobromide emulsion coated at a coverage of about 60 mgs./ft. of silver and about 50 mgs./ft. of gelatin; and

9. a layer containing 4'-methylphenyl hydroquinone dispersed in gelatine and coated at a coverage of about l0 mgs./ft." of 4'-methyl-phenyl hydroquinone and about 30 mgs./ft. ofgelatin. Y Y

The image-recording and image-receiving elements may incorporate other strata and coatings commonly employed in photographic products of this type such as optical coatings for preventing halation and reflection and otherwise improve the optical properties of the sheet material and to facilitate and improve exposure and viewing of the final image. For further details and examples of the composition and structure of image-recording and image-receiving sheets suitable for incorporation in the film unit of the invention reference may be had to the copending U.S. Pat. Application of Edwin H. Land, Ser. No. 638,817, filed May 16, 1967 and now U.S. Pat. No. 3,415,646.

The embodiment of the film unit illustrated and described herein is adapted to be exposed and processed to produce a multicolor dye transfer image in a dyeable polymeric layer located between a transparent film on which the dyeable polymeric layer is supported and an opaquelayer located between the image and the photosensitive medium. This opaque layer comprises the liquid contents 18 of container 16 provided in sufficient quantity to form a layer of predetermined thickness, e.g., of the order of 0.004 inch, when distributed uniformly between the sheets over an area at least coextensive with opening 22 in binding element 20. In order to insure that the quantity of liquid 18 supplied in the container is at least sufficient to form a layer of the desired minimum thickness and extent, the processing liquid is provided in a quantity in excess of the minimum amount required. The processing liquid contained in container 16 comprises an aqueous alkaline solution having a pH at which the dye developers are soluble and diffusible and contains an opacifying agent in a quantity sufficient to mask the dye developers retained in the image-recording layer (laminate) subsequent to processing; and a film-forming, viscosity-increasing agent or agents to facilitate rupture of the container and distribution of the liquid processing composition and help in maintaining the layer of processing composition as a structurally stable layer tending to bind the sheets to one another.

As a general rule, the opacifying agent will be present in the layer of liquid spread between the transparent image-receiving sheet and the opaque image-recording sheet in a concentration sufficient to prevent further exposure of the imagerecording medium by actinic radiation transmitted by the transparent image-receiving sheet. Because the silver halide emulsion or emulsions comprising the image-recording strata are thus protected against exposure by incident actinic radiation at one major surface by the opaque processing composition and at the remaining major surface by the opaque support sheet, it is possible to process the film unit subsequent to distribution of the liquid processing composition in the presence of actinic radiation and thereby eliminate the need to provide a processing chamber within the camera and/or make it possible to withdraw the film unit from the camera almost immediately following distribution of the processing liquid. Binding element 20, strip 44, and the material comprising container 16 are also formed of a material opaque to actinic radiation to prevent exposure of the image-recording medium by light entering the laminated assembly at the edges thereof. The opacifying agentis selected for its suitability as a background for viewing the dye-transfer image formed in the dyeably polymeric layer as well as for its opaque property. Another factor considered in the selection of the opacifying agent is the requirement that it does not interfere with the formation and color integrity of the dye-transfer image in the image-receiving sheet and that the agent be aesthetically pleasing and does not provide a noisey background that may degrade the image or detract from the information content thereof. Opacifying agents particularly desirable for incorporation in the liquid processing composition are those providing a white background for viewing the transfer image and particularly those compositions conventionally employed to provide a background for photographic reflection prints and having optical properties particularly suited for the reflection of incident radiation.

As examples of suitable opacifying agents mention may be made of barium sulfate, zinc oxide, titanium dioxide, barium stearate, silver flake, silicates, alumina, zirconium oxide, zirconium acetyl acetate, sodium zirconium sulfate, kaolin, mica, and the like. An opacifying agent especially preferred because of its highly reflective properties is titanium dioxide and, where it is desired to increase the opaqueness of the processing composition containing, for example, titanium dioxide, beyond that ordinarily obtained, an additional opacifying agent such as carbon black may be added in a concentration of about one part carbon black to 100-500 parts titanium dioxide. A liquid processing composition suitable for incorporation in container 16 for use in combination with sheet materials of the type disclosed in the foregoing example is as follows:

grams 3.4 grams grams gram grams Reference may be had to the aforementioned copending aplplication for additional details and examples of liquid processing compositions adapted for incorporation of the invention to effect the process thereof.

Subsequent to exposure, film unit is processed as illustratedlin FIGS. 4 and 5 of the drawings, by moving the film unit with container 16 foremost relative to and between a pair of juxtaposed members for applying compressive pressure first to the container to eject the fluid contents of the container between the photosensitive and image-recording sheets 12 and 14 and then spread processing liquid 18 toward the trailing end of the film unit as a uniform, thin layer between sheets over an area at least coextensive with opening 22 in binding element 20. As previously noted, the processing liquid includes an agent for increasing the viscosity of the liquid so as to promote opening of the discharge passage of the container throughout substantially its entire length and facilitate the discharge of the liquid from the container and spreading of the liquid between the sheets. For this purpose, the liquid should be quite viscous and contain the film-forming material in quantities sufficient to impart a viscosity in excess of 1000 centipoises at a temperature of C. and preferably of the order of 1000 to 200,000 centipoises at said temperature.

Preferred means for spreading the processing liquid in a thin layer of uniform predetermined thickness comprise a pair of cylindrical rolls 46 mounted in juxtaposition for rotation about axes located in a common plane and biased toward one another and/or mounted a fixed maximum distance apart so as to apply compressive pressure to the container and elements of the film unit during movement thereof between the rolls. During movement of the film unit between rolls 46, compressive pressure is initially applied to container 16 generating hydraulic pressure in liquid 18 effecting the rupture of the bond between longitudinal marginal sections 38 of the container and the discharge of liquid 18 in the form of an elongated mass between sheets 12 and 14 at leading end marginal portions 40 and 42 thereof. Continued movement of the film unit relative to and between spread rolls 46 causes advancement of the mass of liquid between the sheets toward the opposite endthereof and spreading of the liquid as a thin layer 48 of predetermined thickness between and in contact with the facing surfaces of the sheets. A number of expedients are possible for controlling the thickness of the layer of processing liquid distributed between sheets including means in the processing apparatus for appropriately gapping or spacing apart spread rolls 46 and/or components of the film unit capable of performing this function. The film unit illustrated in the drawings is adapted to be employed with cylindrical rolls with the thickness of the liquid layer 48 being controlled, as illustrated in FIGS. 4 and 5, by components of the film unit itself. The spacing between spread rolls 46 and hence the thickness of the layer of processing liquid is determined by the thickness of the film unit at the lateral margins thereof. This thickness is in turn a function of the thickness of the photosensitive and second sheets 12 and 14 and the thickness of lateral edge portions24 of binding element 20. Since the photosensitive and second sheets are of substantially uniform thickness throughout, the thickness of layer 48 of processing liquid is determined by the thickness of binding element 20 and is approximately twice the thickness of the binding element. In a typical film unit, for example, the binding element may have a thickness of the order of 0.002 inch and provide for spreading of the processing liquid in a layer having an initial depth of the order of 0.004 inch.

Spreading of the processing liquid to the edges of the area defined by opening 22 in the binding element and formation of a transfer image extending to the edges of this area may be further insured by embossing the image-receiving sheet 14 at its margins to displace marginal portions 32 and 42 out of the plane of the medial portion of sheet 14 toward sheet 12 by a distance or depth approximating the thickness of binding element 20 or, one half of the desired initial thickness of the layer of processing liquid. This construction provides for the formation of a layer of processing liquid extending substantially to the lateral edges of opening 22 in the binding element. To further insure the formation of a layer of processing liquid extending at least to the lateral edges of the opening in the binding element, the edge sections of lateral edge portions 24 and end portion 28 secured to marginal portions 32 and trailing end section 36 of sheet 14 are wider than the sections of lateral edge portions 24 and end portion 28 secured to marginal portions 30 and trailing end section 34 of sheet 12. Strip 44 is also narrower than end portion 26 and as a result of this construction, during spreading of the processing liquid between sheets 12 and 14, the inner surfaces of the sheets will be spaced apart in lateral and end regions extending outside of the edges of opening 22 allowing processing liquid to enter these regions and provide a reservoir of liquid for effecting image-formation within the region of the exposed imagerecording medium immediately adjacent the lateral and end edges of opening 22. 4

Still another factor contributing to the assurance of a complete spread is the presence of an excess quantity of the processing liquid. The processing liquid is initially spread as shown in H05. 4 and 5 in a layer having a depth approximately twice the thickness of the binding element and calculated to provide aqueous liquid sufficient to permeate the layer containing the photosensitive medium and effect formation of a diffusion transfer image. As the liquid permeates the photosensitive layer and is absorbed and/or dissipated by sheets 12 and 14, the thickness of layer 48 is reduced and the film-forming agent becomes increasingly solid to provide a dimensionally stable opaque layer providing a background for the transfer image and tending to adhere the sheets to one another to form a laminate in which the integrity of the film unit structure is preserved.

As previously noted, the film unit of the invention is designed to be processed by movement between spread rolls 46 to distribute the processing liquid toward the trailing end of the film unit in a layer that is continuous, is of uniform depth and extends throughout the entire area within opening 22 of binding element 20. During spreading, liquid 18 is advanced between the sheets as a mass located immediately ahead of spread rolls 46 and extending from side-to-side of the region defined by opening 22. The binding elements at the lateral margins of the sheets function to prevent escape of the processing liquid and also air, so that air, located between the sheets during spreading of the processing liquid, must be advanced ahead of the mass of liquid and must be permitted to escape at the trailing end of the film unit or it will tend to inhibit the advancement of the mass of liquid.

As previously noted, in order to insure distribution of the liquid in a layer of uniform, minimum, predetermined depth over the entire exposed region to the trailing end thereof and allow some tolerance in the manufacture and filling of the container as well as the depth of the layer of liquid, it is considered necessary to provide excess processing liquid. This makes it necessary to provide for the collection and retention of excess processing liquid within the film unit at the trailing end thereof and prevent the caustic liquid from escaping and contaminating the apparatus, e.g., camera, in which the film unit is processed, or from coming into contact with the operator. Collection and retention of the processing liquid is accomplished by providing a space or spaces within the film unit in which the processing liquid is trapped or collected and from which the processing liquid cannot be squeezed by the pressure-applying members employed to spread the liquid. The liquid collecting and retaining means must not only retain excess processing liquid within the film unit, but at the same time are required to release air from the film unit so that it does not interfere with spreading of the processing liquid.

In the preferred form of the film unit shown in the drawings, excess processing liquid is required to be collected and retained within trapping spaces provided within the bounds of the trailing end region of the film unit, that is, between the edge of the image area and the trailing edge of the film unit. it will be apparent that not only is the space available severely limited but that an excess liquid reservoir will be located in close proximity to the image-containing region between the sheets, thereby presenting additional problems. First, the liquid collecting and retaining (also termed trapping) system must be designed to prevent escape of the liquid and, accordingly, binding element 20 which forms a part of the liquid collecting and retaining system is preferably formed of a substantially liquid-impermeable material, such as a polymeric film, waterproof paper, or the like which is also substantially impermeable to gas. This means that air, advanced between the sheets ahead of the processing liquid, may also tend to be trapped, together with excess processing liquid, interfering with the complete spread of liquid; and accordingly, provision must be made for releasing the air without permitting excess liquid to escape.

A second problem is the backflow of excess processing liquid from the reservoir or trapping means space the invention, the image area due to either or both the tendency for trapped air to be compressed by the pressure-applying members and then expand after movement of the film unit from between the pressure-applying members and any tendency of the sheet materials to stretch under pressure and generate hydraulic pressure within the trapped liquid. A third problem which has already been noted is the presence of the reservoir of excess processing liquid immediately adjacent and/or in direct communication with the space between the sheets containing the image and the resultant tendency for the liquid to migrate from the reservoir into the image-containing area where it may adversely effect the image.

According to the present invention, the answer to the foregoing problems lies in the trapping means of the invention, shown in the drawings as comprising narrow, longitudinal portions of trailing end section 36 of sheet 14 embossed inwardly toward sheet 12 to form relatively short longitudinal ribs 54 extending from the trailing edge of sheet 14 to approximately the trailing edge of sheet 12, the latter underlying trailing end portion 28 of binding element 20. The trailing end section of sheet 14 is preferably provided with a multiplicity of uniformly spaced ribs 54 including at least two ribs, each located closely adjacent a lateral edge of sheet 14. During spreading of the processing liquid, ribs 54 function to space intermediate portions of trailing end section 36 apart from trailing end portion 28 of binding element 20 to provide spaces between sheet 14 and element 20 for collecting and retaining excess processing liquid. The problem of flowback and/or migration of the trapped excess processing liquid into the image area from the trapping spaces is solved by embossing a narrow transverse portion of section 36 to form a transverse rib 52, extending from edge to edge of sheet 14 and joined to the ends (leading) of longitudinal ribs 54. Transverse rib 52 functions to eliminate the spacing between sheet 14 at rib 52 and binding element 20 as the rib passes between the pressure-applying members, thereby squeezing substantially all processing liquid from between the sheet and binding element in the region of the rib. The additional pressure thus applied to the sheet 14 and binding element produces an extremely strong bond between the wet surfaces of the sheet and element in the region of rib 52, effectively preventing separation of the sheet and element and flowback or migration of the processing liquid trapped beyond the transverse rib between the longitudinal ribs.

The ribs formed in trailing end section 36 of sheet 14 also provide for release of air from the trapping spaces during spreading of the processing liquid. It will be apparent that each rib 54 appears, when viewed from the outside of the sheet; as a recess or groove 56 which cooperates with the facing surface of trailing end portion 28 to form a longitudinal conduit or channel 56 communicating with the trapping spaces at the trailing end of sheet 14 and extending therefrom toward the leading end of the film unit where each channel or conduit connects to the channel or conduit 58 formed by transverse rib 52. A number of expedients are suggested for releasing air from the longitudinal or transverse channels 56 and 58. For example, retaining element 20 may be perforated or slit in regions underlying channels 56 and 58 to provide openings through which air may pass. These openings, designated 60, may be located at the lateral edges of the film unit as shown in FIGS. 1 and 2, where they communicate with transverse conduit 58 at the ends thereof; and/or openings, designated 62, may be located at the junctures of channels 56 and 58. Openings 60 and 62 are preferably in the form of pinholes or very fine slits that are almost invisible, yet will readily pass air while resisting the passage of the viscous processing liquid. In another embodiment, narrow regions of trailing end portion 28 extending from transverse channel 58 to the trailing end of opening 22 in binding element 20 may be left unbounded to sheet 14 and thereby provide for escape of air from, the transverse conduit. Channels 56 communicate with the trapping spaces at the trailing end of sheet 14 so that air is required to pass around the trailing edge of the sheet between the latter and trailing end portion 28 by way of spaces which will readily pass air but are so restricted as to prevent the passage of the substantially more viscous processing liquid.

During processing of the film unit, as shown in FIGS. 4 and 5, the processing liquid is advanced as a mass between sheets 12 and 14 by and ahead of pressure-applying rolls 46 toward the trailing end of the film unit and any excess processing liquid is spread beyond the trailing edge of the image area and then the trailing edge of sheet 12 between trailing end section 36 of sheet 14 and trailing end portion 28 of element 20. As the pressure rolls pass over the trailing end section of the film unit, they press the inner facing surface of trailing end portion 28 against transverse rib 52 securely laminating the binding element to the second sheet in the region of rib 52 by virtue of the fact that these portions have been wetted by the liquid so as to activate the adhesive properties of the adjacent strata and there is no layer of liquid between the strata to weaken the bond formed by pressing the sheets and strata together. Moreover, the additional thickness of the film unit in this region provides for the application of increased compressive pressure, further insuring the formation of a secure bond between the sheets in the region of the trailing edge. Ribs 50, being incompressible function to hold apart the facing surfaces of sheet 14 and trailing end portion 28 of binding element 20 in the same region, thereby providing a space into which the excess processing liquid is free to flow. Ribs 50 extend to the trailing edge of sheet 14 and cooperate to maintain the space within the binding element between the trailing edge of sheet 12 and the trailing edge of sheet 14 required to enable the excess processing liquid to flow from between the sheets into the trapping spaces between the ribs.

It should be noted and appreciated that the novel liquid collecting and retaining system of the invention provides substantially the largest possible trapping space within the confined space available within the bounds of the trailing end margins of the film unit and that this space and the reservoir contained therein are located beyond the trailing edge of the photosensitive sheet of the film unit and at a maximum distance from the image-containing space between the sheets. Moreover, the transport system provides for a maximum security seal at the trailing end of the image-containing space insuring that excess processing liquid and/or air cannot migrate back into the image-containing space to impair the image contained between the sheets. Trapping of excess processing liquid is effected within the region of the trailing end border of the laminated product in such a way as to be unobtrusive and not to impair the overall appearance or utility of the photographic print which the product comprises, and as an additional feature, the photosensitive sheet which, particularly when designed to produce a color image, represents a major portion of the total cost of the film unit, is shorter than the second sheet, thus representing a substantial cost saving when large numbers of film units are considered.

Since certain changes may be made in the above product without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic film unit adapted to be processed by moving said film unit, leading end foremost, relative to and between a pair of pressure-applying members to distribute liquid processing composition within said film unit toward the trailing end thereof, said film unit comprising, in combination: a photosensitive sheet including a layer of photosensitive image-recording material coated on a support sheet and having a trailing end section; a second sheet having a trailing end section; and retaining means securing said sheets in face-to-face relation with said trailing end section of one of said sheets extending beyond the trailing edge of the other of said sheets; said retaining means including a retaining sheet engaged around and secured to the outer surfaces of said trailing end sections of said photosensitive and second sheets; narrow portions of said trailing end section of said one sheet being embossed toward said other sheet to form a plurality of raised ribs on one side of said one sheet and corresponding grooves in said opposite side thereof extending from said trailing edge of said other sheet to the trailing edge of said one sheet for spacing apart said pressureapplying members to provide a space between said trailing end section of said one sheet and said retaining sheet for collecting said processing liquid distributed toward the trailing end of said film unit beyond said trailing edge of said other sheet.

2. A photographic film unit as defined in claim 1 wherein said retaining sheet is secured to said outer surface of said one sheet in regions surrounding said grooves, and the latter cooperate with said retaining sheet to form channels for conducting air from said space between said one sheet and said retaining sheet.

3. A photographic film unit as defined in claim 1 wherein said raised ribs include at least two lateral ribs, each located near a lateral edge of said first sheet.

4. A photographic film unit as defined in claim 3 wherein said raised ribs include at least another rib located intermediate said lateral ribs.

5. A photographic film unit as defined in claim 1 wherein a narrow transverse portion of said trailing end section of said one sheet is embossed toward said other sheet to form a raised transverse rib on one side of said one sheet and a corresponding groove in said opposite side thereof extending from side to side of said one sheet and located adjacent said trailing edge of said other sheet.

6. A photographic film unit as defined in claim 5 wherein the first-mentioned ribs are joined to said transverse rib.

7. A photographic film unit as defined in claim 6 wherein said retaining sheet is secured to said outer surface of said one sheet in regions thereof surrounding said narrow portions and the latter cooperate with said retaining sheet to form channels for conducting air from said space between said one sheet and said retaining sheet.

8. A photographic film unit as defined in claim 6 including at least three of said first-mentioned ribs, two of which comprise lateral ribs each located near a lateral edge of said one sheet, and the remaining first-mentioned ribs being located between said lateral ribs.

9. A photographic film unit as defined in claim 1 wherein said one sheet is transparent and said other sheet is said photosensitive sheet.

10. A photographic film unit as defined in claim 1 wherein: said photosensitive and second sheets are rectangular and arranged with their lateral edges in substantial alignment; said retaining sheet is generally rectangular and is formed with a rectangular medial opening surrounded by lateral and end edge sections secured to said outer surface of said one sheet at the lateral and end margins thereof; portions of said lateral edge sections and the trailing edge section of said retaining sheet being folded around the lateral and trailing end edges of said one sheet and secured to the outer surface of said other sheet at the lateral and trailing end margins thereof with said ribs underlying said trailing end section of said retaining sheet.

11. A photographic film unit as defined in claim 10 wherein said medial opening includes a trailing edge and said trailing edge of said other sheet is located between said trailing edge of said medial opening and the ends of said ribs furthest from said trailing edge of said one sheet.

12. A photographic film unit as defined in claim 11 wherein said medial opening includes a trailing edge, and a narrow, transverse portion of said trailing end section of said one sheet is embossed toward said other sheet to form a raised transverse rib extending from side to side of said one sheet and located adjacent said trailing edge of said other sheet underlying said trailing end section of said retaining sheet.

13. A photographic film unit as defined in claim 9 wherein said second sheet is transparent and said other sheet is said photosensitive sheet. 

2. A photographic film unit as defined in claim 1 wherein said retaining sheet is secured to said outer surface of said one sheet in regions surrounding said grooves, and the latter cooperate with said retaining sheet to form channels for conducting air from said space between said one sheet and said retaining sheet.
 3. A photographic film unit as defined in claim 1 wherein said raised ribs include at least two lateral ribs, each located near a lateral edge of said first sheet.
 4. A photographic film unit as defined in claim 3 wherein said raised ribs include at least another rib located intermediate said lateral ribs.
 5. A photographic film unit as defined in claim 1 wherein a narrow transverse portion of said trailing end section of said one sheet is embossed toward said other sheet to form a raised transverse rib on one side of said one sheet and a corresponding groove in said opposite side thereof extending from side to side of said one sheet and located adjacent said trailing edge of said other sheet.
 6. A photographic film unit as defined in claim 5 wherein the first-mentioned ribs are joined to said transverse rib.
 7. A photographic film unit as defined in claim 6 wherein said retaining sheet is secured to said outer surface of said one sheet in regions thereof surrounding said narrow portions and the latter cooperate with said retaining sheet to form channels for conducting air from said space between said one sheet and said retaining sheet.
 8. A photographic film unit as defined in claim 6 including at least three of said first-mentioned ribs, two of which comprise lateral ribs each located near a lateral edge of said one sheet, and the remaining first-mentioned ribs being located between said lateral ribs.
 9. A photographic film unit as defined in claim 1 wherein said one sheet is transparent and said other sheet is said photosensitive sheet.
 10. A photographic film unit as defined in claim 1 wherein: said photosensitive and second sheets are rectangular and arranged with their lateral edges in substantial alignment; said retaining sheet is generally rectangular and is formed with a rectangular medial opening surrounded by lateral and end edge sections secured to said outer surface of said one sheet at the lateral and end margins thereof; portions of said lateral edge sections and the trailing edge section of said retaining sheet being folded around the lateral and trailing end edges of said one sheet and secured to the outer surface of said other sheet at the lateral and trailing end margins thereof with said ribs underlying said trailing end section of said retaining sheet.
 11. A photographic film unit as defined in claim 10 wherein said medial opening includes a trailing edge and said trailing edge of said other sheet is located between said trailing edge of said medial opening and the ends of said ribs furthest from said trailing edge of said one sheet.
 12. A photographic film unit as defined in claim 11 wherein said medial opening includes a trailing edge, and a narrow, transverse portion of said trailing end section of said one sheet is embossed toward said other sheet to form a raised transverse rib extending from side to side of said one sheet and located adjacent said trailing edge of said other sheet underlying said trailing end section of said retaining sheet.
 13. A photographic film unit as defined in claim 9 wherein said second sheet is transparent and said other sheet is said photosensitive sheet. 